Thorax:Muscle:Diaphragm
The diaphragm is the dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm's muscular fibres originate around the circumference of the thoracic outlet, passes upwards into two domes before converging to a common insertion point of the central tendon. The central tendon, is a thin but strong aponeurosis, inseparable from the fibrous pericardium. The muscle slips can be grouped according to their origins: * sternal - arises from two strips under the xiphoid process * costal - arise from the inner surfaces of the costal cartilages of the 6th ribs on either side which interdigitates with the transversus abdominus muscles * lumbar - arise from the aponeurotic arches (lubocostal arches) and from the lumbar vertebrae (crura) The crura are tendinous structures attached to the anterolateral surfaces of the bodies of the upper lumbar vertebrae. * right crus is longer than the left, and arises from the anterior surfaces of the bodies of L1-3 * left crus arises from the corresponding portions of L1-2 Three ligaments: * medial lumbocostal arch (medial arcuate ligament) - a tendinous arch that covers psoas major; continuous medially with left crura; attached to the L2 vertebral body and in the front of the transverse process of L1 and L2 * lateral lumbocostal arch (lateral arcuate ligament) - covers quadratus lumborum; attached medially to the L1 transverse process and attached laterally to the middle of the 12th rib * The medial margins of the two crura pass forwards and medially. They meet in the midline to form an arch in front of the aorta called the median arcuate ligament. Diaphragmatic Aperture: A series of apertures that permit the passage of structures between the thoracic and abdominal cavities: The aortic hiatus lies at the level of T12. It is osseo-aponeurotic opening between the median arcuate ligament and the vertebral column. * aorta * azygous vein * thoracic duct The oesophageal hiatus allows the oesophagus to pass through and lies at T10 within the right crus. It slightly to the left of midline. * oesophagus * vagus nerves * small oesophageal arteries of left gastric The vena caval foramen situated at the level of T8-9. It is quadrilateral and placed at the junction of the right and middle leaflets of the central tendon. * inferior vena cava * branches of the right phrenic nerve ** note: left phrenic nerve directly pierces the dome of the left hemidiaphragm The lesser diaphragmatic apertures allow the passage of smaller structures from thethoracic cavity to abdominal cavity across the diaphragm. They are very much smaller than the other diaphragmatic apertures: * two in the right crus of the diaphragm - transmit greater and lesser right splanchnic nerve * three in the left crus of the diaphragm - transmit greater and lesser left splanchnic nerves as well as the hemiazygos vein * under the medial arcuate ligament - usually transmit the sympathetic trunks * under the lateral arcuate ligament - subcostal nerve and vessels * left phrenic nerve pierces the dome of the left hemidiaphragm * small interval the sternal and costal parts of the diaphragm where the muscular fibers of the diaphragm are deficient allow superior epigastric branch of the internal thoracic artery and lymphatics from the abdominal wall and convex surface of the liver pass through. Action * Inspiration: the fibres contract and the dome descend. In deeper breath, the central tendon depresses and is limited by the stretching of the mediastinum. During contraction, the vean caval foramen opens wider, and venous return increases. The oesophageal opening is held close by the sligh of right crus to discourage reflux. Aortic opening unaffected. * Expiration: passive relaxation. Blood supply * arterial supply ** costal margins - lower five intercostal; subcostal arteries ** abdominal surface - right and left inferior phrenic arteries (from abdominal aorta) ** supply is augmented by superior phrenic artery and musculophrenic artery, pericardicophrenic Nerve supply * each phrenic nerve (C3-5) supplies the ipsilateral hemidiaphragm with motor fibres * lower intercostal nerves supply proprioceptive fibres to the margins * subcostal and phrenic also sensory fibres Variant anatomy * muscle slips * scalloped or serrated appearance - due to individual muscle slips * dromedary diaphragm (hump) * accessory diaphragm